Enchancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) accumulation in Arxula adeninivorans by stabilization of production

Background: In recent years the production of biobased biodegradable plastics has been of interest of researchers partly due to the accumulation of non-biodegradable plastics in the environment and to the opportunity for new applications. Commonly investigated are the polyhydroxyalkanoates (PHAs) poly(hydroxybutyrate) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHB-V). The latter has the advantage of being tougher and less brittle. The production of these polymers in bacteria is well established but production in yeast may have some advantages, e.g. the ability to use a broad spectrum of industrial by-products as a carbon sources. Results: In this study we increased the synthesis of PHB-V in the non-conventional yeast Arxula adeninivorans by stabilization of polymer accumulation via genetic modification and optimization of culture conditions. An A. adeninivorans strain with overexpressed PHA pathway genes for β-ketothiolase, acetoacetyl-CoA reductase, PHAs synthase and the phasin gene was able to accumulate an unexpectedly high level of polymer. It was found that an optimized strain cultivated in a shaking incubator is able to produce up to 52.1% of the DCW of PHB-V (10.8gL-1) with 12.3%mol of PHV fraction. Although further optimization of cultivation conditions in a fed-batch bioreactor led to lower polymer content (15.3% of the DCW of PHB-V), the PHV fraction and total polymer level increased to 23.1%mol and 11.6gL-1respectively. Additionally, analysis of the product revealed that the polymer has a very low average molecular mass and unexpected melting and glass transition temperatures. Conclusions: This study indicates a potential of use for the non-conventional yeast, A. adeninivorans, as an efficient producer of polyhydroxyalkanoates

Investigating yeast cell responses to oestrogen by electrochemical detection

Candida albicans and some other yeast species are known to have an oestrogen binding protein (EBP), which oxidises NAD(P)H to NAD(P)+. 17-oestradiol, when present, binds to the NAD(P)H oxidation site which leads to an accumulation of NAD(P)H. Our previous research has shown that oestrogens can be quantified using Saccharomyces cerevisiae cells as the detection element and a double mediator electrochemical system to measure NAD(P)H. In a modification to the whole cell method, C. albicans cell lysate and a single hydrophilic mediator was used to quantify 17-oestradiol. This paper employs the mediated electrochemical systems to investigate the influence of growth phase on EBP production in C. albicans and the response of cells of different ages to different concentrations of oestrogen. A cell not known to possess EBP (Arxula adeninivorans) was also investigated for its response to 17-oestradiol. As expected, A. adeninivorans did not show a detectable response to 17-oestradiol, but surprisingly, its catabolism was inhibited